It is well known that coal seams have methane, and other light hydrocarbon gases absorbed thereon and contained in the interstices thereof. These gases have been known to explode and cause great disasters during underground mining operations. Efforts have been made to produce the light gases from coal seams in the same manner as hydrocarbonaceous gas would be produced from any other formation. That is, a gas production well is drilled into the coal seam; as part of the well completion procedure, the seam is hydraulically fractured; the water, which usually substantially floods coal seams, is extracted; and, as the pressure in the coal seam subsides by reason of the removal of the water, the light gas is produced.
Methane is currently being produced from unconventional sources, such as coal beds, in the western and southwestern parts of the United States. This is being accomplished by conventional gas well drilling and completion procedures, as aforesaid, including hydraulic fracturing. Because the coal beds contain large quantities of water, the water must be pumped off until the reservoir pressure in the vicinity of the wellbore decreases sufficiently for the methane and other light gases to desorb from the coal surfaces and flow through the natural channels in the coal seam, as well as through fractures induced hydraulically in the seam.
It would, of course, be desirable to improve the efficiency of production of hydrocarbonaceous gas, and it is an important object of this invention to do so.
It is another important object of this invention to increase the amount of hydrocarbonaceous gas produced from coal seams as well as to reduce the time from well completion to the onset of gas production.
An additional object of this invention is to provide means to render coal mining safer, with respect to the danger of fire and explosion caused by the existence of hydrocarbonaceous gases interspersed with the coal.